Photopolymerizable composition stabilized with epoxide compounds and process

ABSTRACT

A stabilized photopolymerizable composition comprising photopolymerizable ethylenically unsaturated monomeric compounds, a photoinitiator and at least one epoxide compound as a stabilizer.

BACKGROUND OF THE INVENTION

This invention relates to stabilized photopolymerizable compositionsbased on photopolymerizable ethylenically unsaturated compoundscontaining benzoin ether initiators. More particularly, this inventionrelates to the use of certain epoxide compounds as stabilizers forphotopolymerizable compositions containing photoinitiators.

Photopolymerizable compositions containing unsaturated materials andphotoinitiating compounds are well known in the art, being particularlyuseful for moldings and coatings. These materials polymerize at lowtemperatures when exposed to actinic radiation. While numerous compoundshave been found useful as photoinitiators for the polymerization ofunsaturated compounds, the ethers of benzoin have found wide-spreadcommercial acceptance. These benzoin ethers exhibit excellent curerates, rendering them particularly attractive where rapid hardening isdesirable. The use of benzoin ethers as photopolymerization initiatorsis described in U.S. Pat. No. 2,448,828.

While the benzoin ethers are widely used because of their excellentcuring properties, they are not wholly satisfactory with regard tostorage stability. Thus, unsaturated systems to which benzoin ethers areadded have considerably diminished dark storage stability and will gellprematurely in many systems where storage is a key factor.

Various attempts have been made to remedy this deficiency of the benzoincompounds by including stabilizing additives in the photopolymerizablecomposition. For example, U.S. Pat. No. 3,814,702 teachesphotosensitizing compositions comprising a benzoin ether, an organicacid and a solvent; optionally, a weak reducing agent may be included inthe photosensitizing composition. Other multi-component stabilizingsystems are described in U.S. Pat. No. 3,819,495, which discloses acopper compound soluble in polyester resin and an organic compoundhaving ionically-bound chlorine or capable of forming chlorine ions insitu as stabilizers for polyester resins containing benzoin ethers,while U.S. Pat. No. 3,819,496 discloses similar systems employing aniron and/or manganese compound instead of the copper compound.

Other compounds have been added to benzoin ether systems as cureaccelerators. For example, Japan Kokai 73 00,983 discloses the use ofdialkylaminobenzoins in conjunction with benzoin methyl ether as curingagents for polyester resins, while Japan Kokai 73 75,638 teachesmixtures of benzoin alkyl ether andp,p'-bis(dialkylamino)thiobenzophenone as curing agents that providecolored products. In German Offen. No. 2,263,804, the addition ofascorbic acid or thiourea to benzoin ethyl ether to reduce the exposuretime of photopolymer printing reliefs is disclosed. While functioning toaccelerate curing, many of these compounds are known to decrease thestorage stability of the system.

Furthermore, additives to benzoin ether systems to function asstabilizers against discoloration have been proposed. Thus, U.S. Pat.No. 2,647,080 describes the addition of allyl glycidyl ether to systemscontaining halogen-free acrylate and acyloin ether initiators in orderto prevent discoloration of the systems by light.

Now it has been found in accordance with this invention that selectedepoxide compounds are excellent stabilizing agents forphotopolymerizable compositions containing photoinitiators. Thesestabilizing agents function to improve the dark storage capability ofthe composition without significantly detracting from the cure rate.

SUMMARY OF THE INVENTION

The stabilized photopolymerizable composition of this inventioncomprises an ethylenically unsaturated monomeric compound, aphotoinitiator and at least one selected epoxide compound.

DETAILED DESCRIPTION OF THE INVENTION

More in detail, the photopolymerizable composition of this inventioncomprises at least one photopolymerizable ethylenically unsaturatedcompound containing a photoinitiator in an amount sufficient to initiatephotopolymerization and a stabilizing amount of an epoxide compoundhaving the formula ##STR1## wherein: R¹ and R² are

a. independently selected hydrogen, alkyl of 1 to 18 carbon atoms, arylof 6 to 13 ring carbon atoms, ##STR2## where R³ is alkenyl of 2 to 6carbon atoms and R⁴ is alkylene of 1 to 4 carbon atoms or cycloalkenyloxide of 5 or 6 ring carbon atoms, with the proviso that both R¹ and R²cannot be hydrogen; or

b. together with the adjacent epoxy carbon atoms form a cyclichydrocarbon having a total of 5 to 7 ring carbon atoms;

R⁵ is hydrogen or alkyl of 1 to 4 carbon atoms;

X is oxygen, ##STR3## where y is an integer from 1 to 4, m being 2; or##STR4## m being 1; and n is zero or 1.

Illustrative of the epoxides I are epoxypropane; 1,2-epoxybutane;1,2-epoxyoctadecane; 3,4-epoxyheptane; 1,2-epoxy 4-methyldecane; styreneoxide; naphthalene oxide; cyclohexene oxide; glycidyl acrylate; vinylcyclopentene dioxide; vinyl cyclohexene dioxide; methylenebis-(cyclohexane oxide); butylene bis-(cyclohexane oxide);3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate;3,4-epoxycyclohexylbutyl-3,4-epoxycyclohexane carboxylate;3,4-epoxycyclohexane acetamide; bis-(2,3-epoxycyclopentyl)ether;bis-(3,4-epoxy-6-methylcyclohexylmethyl)adipate;2-(3,4-epoxycyclohexyl)-5,5-spiro-(3,4 epoxy)cyclohexane-m-dioxane; etc.

The epoxides I are known compounds, many of which are commerciallyavailable. Alternately they are readily prepared by methods described inthe literature. For example, some of them can be prepared by oxidationof the corresponding olefin with a per-acid as described by Y. R. Nanesand P. Bachman in Helv. 28, 1227 (1945). Oxidation of the olefin withvanadium pentoxide and hydrogen peroxide to provide epoxides isdisclosed by W. Treibs in Ang. Chemie 52, 698 (1939), while P. Karrerand H. Sturzingler in Helv. 29, 1829 (1946) teach oxidation of olefinswith hydrogen peroxide.

The stabilizer is generally employed in an amount from about 0.01 toabout 30% by weight of the initiator and preferably from about 0.5 toabout 5.0% by weight of the initiator. The initiator is generallyemployed in an amount from about 0.01 to about 30%, and preferably fromabout 1 to about 5% loading by weight of the total composition.

Photopolymerizable ethylenically unsaturated compounds useful in thecompositions of this invention include acrylic, α-alkacrylic andα-chloroacrylic acid compounds such as esters, amides and nitriles.Examples of such compounds are acrylonitrile, methacrylonitrile, methylacrylate, ethyl acrylate, methyl methacrylate, isobutyl methacrylate,2-ethyl-hexyl acrylate, methacrylamide and methyl α-chloroacrylate. Alsouseful, although not preferred, are vinyl and vinylidene esters, ethersand ketones. Additionally, compounds having more than one terminalunsaturation can be used. Examples of these include diallyl phthalate,diallyl maleate, diallyl fumarate, triallyl cyanurate, triallylphosphate, ethylene glycol dimethacrylate, glycerol trimethacrylate,pentaerythritol triacrylate, pentaerythritol tetraacrylate,trimethylolpropane triacrylate, methacrylic anhydride and allyl ethersof monohydroxy or polyhydroxy compounds such as ethylene glycol diallylether, pentaerythritol tetraallyl ether, and the like. Nonterminallyunsaturated compounds such as diethyl fumarate can similarly be used.

The derivatives of acrylic acid, which include the derivatives ofmethacrylic acid, are particularly well suited to the practice of theinvention and are consequently preferred components as monomers inmonomer-containing polymerizable systems and as reactive centers inpolymerizable polymers.

The photoinitiators suitable for use in the practice of this inventioninclude various carbonyl compounds including the acetophenones,benzophenones, etc.; the acyloins; etc. Preferred are the benzoin etherinitiators of the formula ##STR5## wherein R₁ and R₂ are, independentlyfrom one another, selected from hydrogen atoms, or aliphatic or aromatichydrocarbon radicals, and R₃ and R₄ are, independently from one another,benzene nuclei, or benzene nuclei mono-, di- or tri-substituted withalkyl, alkoxy, trihaloalkyl, metahydroxy, alkyenedioxy groups or halogenatoms.

The benzoin ethers are known photosensitizers that may be preparedaccording to the method described by Whitmore in Organic Chemistry, page405, by Fisher in Berichte, 26, 2412 (1893), or by Irvine and Moodie asdescribed in Journal Chemistry Society, 91, 543, (1907).

Among the various benzoin ethers suitable for the purposes of theinvention are in particular the phenyl, cresyl, benzyl, cyclohexylethers thereof and alkyl ethers thereof such as the methyl, ethyl,propyl, isopropyl, butyl and isobutyl ethers, and isomers thereof.

While any of the epoxide compounds having the formula I can be used inthe practice of this invention, preferred are compounds I where R¹ andR² are independently selected hydrogen, alkyl of 5 to 18 carbon atoms;##STR6## where R³ is alkenyl of 3 or 4 carbon atoms and R⁴ is alkyleneof 1 or 2 carbon atoms or cyclohexenyl oxide, or together with theadjacent epoxy carbon atoms form a cyclic hydrocarbon having a total of5 to 7 ring carbon atoms, and those compounds II where R⁵ is hydrogen ormethyl; X is oxygen, ##STR7##

Additionally, the photopolymerizable composition can containantioxidants and stabilizers such as phenylnaphthylamine, etc.

Co-stabilizers can also be employed in the practice of this invention.Thus, nitrogen-containing aromatic compounds such as those disclosed incopending application, U.S. Ser. No. 773,370, filed Mar. 1, 1977, andammonium salts of phosphorus acid as disclosed in copending applicationU.S. Ser. No. 755,286, filed Dec. 29, 1976 now U.S. Pat. No. 4,077,860,can be added to the photopolymerizable composition.

Thus, it is seen that the constitution of photopolymerizablecompositions which can be used in the practice of the invention iswidely variable. However, the compounds enumerated above are purelyillustrative. Materials subject to polymerization by actinic radiationas well as permissable variations and substitutions of equivalentcomponents within particular types of compositions are well known tothose skilled in the art.

The photopolymerizable compositions of this invention have been found tohave markedly enhanced dark-storage capability over correspondingsystems not including the epoxide containing compounds I.

The process can be carried out by mixing a quantity of a photoinitiatingcompound and a stabilizer of the invention with a photopolymerizablecomposition and exposing the resultant mixture to actinic radiation.Alternatively, a one-component system comprising the photopolymerizablecomposition, the stabilizer of the invention and, if desired,appropriate pigmentation, can be stored in the dark for a prolongedperiod of time prior to use without fear of gelation.

A preferred manner of practicing the invention is by the use ofphotopolymerizable molding and coating compositions which consist ofmixtures of unsaturated polymeric compounds and monomeric compoundscopolymerizable therewith. The polymeric compounds can be conventionalpolyesters prepared from unsaturated polycarboxylic acids such as maleicacid, fumaric acid, glutaconic acid, itaconic acid, citraconic acid,mesaconic acid and the like, and polyhydric alcohols such as ethyleneglycol, diethylene glycol, glycerol, propylene glycol, 1,2-butanediol,1,4-butanediol, pentaerythritol, trimethylolpropane and the like. Thecarboxylic acid content can also contain saturated components. Theinclusion of a monobasic fatty acid content, either as such or in theform of a triglyceride or oil, in the photopolymerizable polyestercomposition to comprise an alkyd resin is also acceptable. These resinscan, in turn, be modified by silicones, epoxides, isocyanates, etc., byknown techniques.

The compositions of the instant invention after being prepared in theratios as set out above can be applied to the material to be coated byconventional means, including brushing, spraying, dipping, curtain androll coating techniques, and may, if desired, be dried under ambient oroven conditions to provide coating films on the substrate. The substratecan be of any composition, e.g., wood, metal, paper, plastic, fabric,fiber, ceramic, concrete, plaster, glass, etc.

After the composition is applied to the desired substrate, it is exposedto light radiation having wave lengths of above about 2000 Angstromunits, preferably from about 2000 up to about 8000 Angstroms, and mostpreferably between about 2400 Angstroms and 5400 Angstroms. Exposureshould be from a source located about 1 to 5 inches from the coating fora time sufficient to cause crosslinking of the composition and can rangefrom about 0.1 seconds up to about 1 min./linear ft. Generally, thelight radiation will have power of about 200 watts per linear inch.

The light radiation can be ultraviolet light generated from low, mediumand high pressure mercury lamps. This equipment is readily available andits use is well known to those skilled in the art of radiationchemistry. Other sources include electron beam radiation, plasma arc,laser beams, etc.

In the following examples, which will serve to illustrate the practiceof this invention, all parts and percentages are by weight unlessotherwise specified.

EXAMPLE 1

An epoxide having the formula ##STR8## was added in variousconcentrations to samples of Satomer SR 351 resin containing 3.6% byweight of benzoin isobutyl ether initiator. The epoxide is available asERL-4221 from Union Carbide Chemical Corp. Satomer SR 351 resin istrimethylolpropane triacrylate marketed by Satomer Company. Glass jarswere filled to greater than 90% by volume with the stabilizedcompositions, which were then stored in the dark at 65° C. Stability isreported in Table 1 as the number of days the compositions remainedstable prior to gelation. The symbol ">" indicates that gelation had notoccurred when inspected after the indicated number of days in storage.

                  TABLE 1                                                         ______________________________________                                               Concentration of                                                              ERL-4221             Stability                                         Sample (% by Wt. of Total Formulation)                                                                    (Days at 65° C.)                           ______________________________________                                        1      0                    4.0                                               2      0.04                 37.0                                              3      0.10                 >50.0                                             4      0.20                 >50.0                                             5      0.36                 49.0                                              6      0.62                 48.0                                              7      1.2                  11.0                                              ______________________________________                                    

EXAMPLES 2-6

Various epoxides were added to Satomer SR 351 resin containing 3.6% byweight of benzoin isobutyl ether. Satomer SR 351 resin istrimethylolpropane triacrylate marketed by Satomer Company. Stabilitywas determined as described in Example 1; the results are set forth inTable 2.

                  TABLE 2                                                         ______________________________________                                                           Concentration Stability                                    Ex.  Stabilizer    (% by Wt. of Resin)                                                                         (Days at 65° C.)                      ______________________________________                                        2    ERL-4221      1.0           28.0                                         3    Styrene Oxide 1.4           1.6                                          4    Cyclohexane Oxide                                                                           1.1           7.0                                          5    Glycidyl Acrylate                                                                           1.3           >50.0                                        6    1,2-Epoxydecane                                                                             1.4           43.0                                         ______________________________________                                    

EXAMPLES 7-8

These examples reflect stability tests in pentaerythritol tetraacrylateresin containing 1.2% by weight of benzoin isobutyl ether initiator. Thetesting was carried out following the procedure described in Example 1;the results are reported in Table 3.

                  TABLE 3                                                         ______________________________________                                                             Concentration                                                                 (% by Wt.   Stability                                    Example                                                                              Stabilizer    of Resin)   (Days at 65° C.)                      ______________________________________                                        Control                                                                              None          --          1.0                                          7      1,2-Epoxydecane                                                                             0.05        3.0                                          8      Glycidyl Acrylate                                                                           0.05        3.0                                          ______________________________________                                    

EXAMPLES 9-15

The following stability tests indicate the effect when epoxides incombination with other stabilizers and additives are added to variousresins. The testing was carried out in accordance with the proceduredescribed in Example 1; the results are set forth in Table 4. All theresins contained benzoin isobutyl ether as the initiator.

                                      TABLE 4                                     __________________________________________________________________________                                   Stability                                      Stabilizer and        Initiator                                                                              (Days at 65° C.)                             Concentration as Concentration                                                                          Satomer.sup.1)                                 Example                                                                            Wt. % of Resin   as Wt. % of Resin                                                                      SR 351                                                                             PEA.sup.2)                                                                         PETA.sup.3)                                                                        HDODA.sup.4)                    __________________________________________________________________________    Control                                                                            None             3.6      4.0-5.0                                                                            1.0  1.0  1.0                              9   0.14% ERL-4221   3.6      60.0 --   --   --                              10   0.17% ERL-4221 and                                                                             3.6      >100.0                                                                             --   --   --                                   0.17% 8-Hydroxyquinoline                                                 11   0.17% ERL-4221 and                                                                             3.6      63.0 --   --   --                                   0.17% phenyl-α-naphthylamine                                       12   0.07% ERL-4221 and                                                                             3.6      > 24.0                                                                             >20.0                                                                              1.0  1.0                                  0.07% phenyl-α-naphthylamine                                       13   0.02% ERL-4221 and                                                                             1.2      --   12.0 3.0  1.0                                  0.02% phenyl-α-naphthylamine                                       14   0.02% ERL-4221 and                                                                             1.2      --   --   6.0  1.6                                  0.02% phenyl-α-naphthylamine and                                        0.02% 8-hydroxyquinoline                                                 15   0.17% ERL-4221 and                                                                             3.6       4.0 --   --   --                                   0.17% decyl trimethylammonium                                                 diphenylphosphate                                                        __________________________________________________________________________     .sup.1) Trimethylolpropane triacrylate marketed by Satomer Company.           .sup.2) Pentaerythritol acrylate marketed by Union Carbide Corporation.       .sup.3) Pentaerythritol tetraacrylate marketed by Satomer Company.            .sup.4) 1,6 Hexanediol diacrylate marketed by Celanese Corporation.      

EXAMPLE 16

This example further illustrates the effect of adding an epoxide tovarious resins. Stability was determined as described in Example 1; theresults are set forth in Table 5.

                                      TABLE 5                                     __________________________________________________________________________               Stability                                                                     (Days at 65° C.)                                            Concentration as                                                                         Satomer.sup.1)                                                                      Celanese.sup.2)                                                                     Union Carbide.sup.3)                                                                    Satomer.sup.4)                               Wt. % of Initiator                                                                       TMPTA TMPTA PETA      PETA                                         __________________________________________________________________________    None       4.0   <1.0  <1.0      <2.0                                         2.5% ERL-4221                                                                            82.0  1.0   15.0      1.0                                          __________________________________________________________________________     .sup.1) Initiator loading of 3.6% by weight of Satomer 351, which is          trimethylolpropane triacrylate marketed by Satomer Company.                   .sup.2) Initiator loading of 3.6% by weight of trimethylolpropane             triacrylate marketed by Celanese Corporation.                                 .sup.3) Initiator loading of 1.2% by weight of pentaerythritol triacrylat     marketed by Union Carbide Corporation.                                        .sup.4) Initiator loading of 1.2% by weight of pentaerythritol                tetraacrylate marketed by Satomer Company. The control was not inspected      until 2 days after initiation of storage.                                

COMPARATIVE EXAMPLE

Acrylic acid in various concentrations was added to samples of SatomerSR 351 resin (trimethylolpropane triacrylate) containing 3.6% by weightof benzoin isobutyl ether. Stability was determined as described inExample 1. The results, which are set forth in Table 6, indicate thatacid tends to decrease stability only at abnormally high concentrations.Thus, it appears that the epoxides are not necessarily functioning asacid acceptors in this invention.

                                      TABLE 6                                     __________________________________________________________________________        Concentration of Acrylic Acid                                                                Calculated Acid Number                                                                     Stability                                     Sample                                                                            (% by Wt. of Resin)                                                                          (Milligrams KOH/gram)                                                                      (Days at 65° C.)                       __________________________________________________________________________    1   0              0.26         4.4 (average of                                                                6 samples)                                   2   1.2            9.3          4.0                                           3   2.4            18.6         3.0                                           4   3.5            28.0         4.0                                           5   5.8            45.0         4.0                                           6   10.7           137.0        2.0                                           __________________________________________________________________________

What is claimed is:
 1. In a photopolymerizable composition comprising atleast one photopolymerizable ethylenically unsaturated compound and aphotoinitiating compound, the improvement which comprises incorporatinga stabilizing amount of an epoxide having the formula: ##STR9## where R⁵is hydrogen or alkyl of 1 to 4 carbon atoms and n is zero or
 1. 2. Thecomposition of claim 1 wherein said epoxide is3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate.